The present invention relates to a novel process for the preparation of dicarboxylic acids from (poly)alkylene glycols. More particularly, the present invention relates to the oxidation of (poly)alkylene glycols such as diethylene glycol employing electrochemically generated nickel-oxide hydroxide, NiO(OH).
It is already known to prepare carboxylic acids by chemical oxidation of (poly)alkylene glycols. For example, in U.S. Pat. No. 3,725,290 it was taught that nitric acid will oxidize diethylene glycol to diglycolic acid in high yield. Similarly in U.S. Pat. No. 3,929,873, a process for the heterogeneous platinum catalyzed air oxidation of (poly)ethylene glycols was disclosed. Certain strong chemical oxidants are unsuited for the oxidation of (poly)glycol ethers due to degradation of ether linkages or over-oxidation to the carbonate instead of the acid product.
Electrochemically prepared nickel (III) oxide hydroxide is already known to be suitable for the oxidation of primary alcohols. J. Kaulen et al. in Synthesis, 513 (1979), taught such an electrochemical oxidation of numerous aliphatic alcohols, including furfuryl alcohol, an aromatic ether, Ibid., at 514.
In GB No. 1,051,614, ethylene glycol, which contains no ether linkages, was oxidized by use of electrochemically prepared nickel-oxide hydroxide and a nickel anode. The product was glycolic acid.
G. Vertes et al., Tet. 28, 37-42 (1972), reported that no chemical difference could be detected between active nickel hydroxide prepared chemically and the active species formed on a nickel hydroxide electrode. Further research by the present inventors illustrated that chemically prepared NiO.sub.2 H, prepared by action of hydrogen peroxide on aqueous nickel salt solutions was not suitable in oxidizing ether alcohols, especially (poly)alkylene glycols. The products formed included unacceptable amounts of formates, carbonates and other over-oxidation or ether-cleavage products.